PROJECT SUMMARY ? Project 1 Cowan A major challenge for treating drug addiction is the poor understanding of the molecular mechanisms by which drug use produces persistent changes in brain function that facilitate drug seeking even after long periods of abstinence. Chronic drug use engages an epigenetic process, involving the chromatin-remodeling enzyme, histone deacetylase 5 (HDAC5), in striatal medium spiny neurons that functions to limit the development of multiple addiction-related behaviors, including reinstatement of cocaine and heroin seeking. However, HDAC5?s regulation and function during and after drug taking is complex and poorly understood. Cocaine and heroin produce reactive oxygen and nitrogen species (ROS/RNS) that alter the redox state of the cell, and redox-mediated cysteine thiol modifications alter the structure/function of target proteins, including class IIa HDACs. Repeated treatment of animals or humans with the antioxidant and glutathione precursor, N- acetylcysteine (NAC), reduces the vulnerability to reinstatement of cocaine and heroin seeking, and NAC blocks ROS-promoted HDAC5 nuclear export. The long-term goal of Project 1 is to understand the redox protein signaling and epigenetic mechanisms by which HDAC5 and NAC regulate heroin and cocaine relapse behaviors in hopes of identifying better therapeutic strategies for the treatment of drug addiction. We hypothesize that: (1) cocaine- and heroin-produced oxidative stress modifies HDAC5 cysteine thiol groups in the nucleus accumbens, which promotes nuclear export and reduces the anti-relapse actions of HDAC5, and (2) the anti-relapse effects of repeated NAC treatment are due, at least in part, to its ability to protect HDAC5 from ROS signaling events that promote nuclear exclusion and changes in gene expression. We will use cutting-edge mouse genetics and cre-dependent viral tools that allow for time-delimited and cell-type specific manipulation of nucleus accumbens core neurons during drug taking and relapse events. Aim 1. Molecular and Cellular Mechanisms: In this aim, we will determine how cocaine and heroin SA regulate HDAC5?s redox-sensitive posttranslational modifications, subcellular distribution, genomic binding and regulation of gene expression. Aim 2. Circuit Specificity: In this aim, we will take a cutting-edge molecular genetic approach to dissect the cell-type specific roles for HDAC5 to negatively-regulate cocaine and heroin drug seeking. Aim 3. Treatment: In this aim, we will analyze the regulation of HDAC5 by NAC, and test the role of HDAC5 in the long-lasting ability of NAC to reduce reinstatement of heroin and cocaine seeking.